Combustion chamber



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Patented Mar. 4, 1930 UNITED STATES PATENT OFFICE WILLIAM B. EARNSHAW, OF DAYTON, OHIO, AND ROBERT N. JANEWAY, OF DETROIT,

MICHIGAN, ASSIGNORS TO GENERAL MOTORS RESEARCH CORPORATION, OF DE- TROIT, MICHIGAN, A CORPORATION OF DELAWARE COMBUSTION CHAMBER Application iled May 31,

V This invention relates to combustion chambers of internal combustion engines.

The objects of the invention are to reduce detonating tendency and improve smoothness of operation, thereby permitting higher compression of the charge admitted to the cylinder than is possible with the hitherto usual form of combustion chamber.'

Normal combustion is progressive. From the point of ignition of the charge in an engine cylinder flame spreads equally in all directions. As the charge burns the increasing volume and pressure of the'burning gas compresses the remaining unburnt gas ahead of the ilame, which moves ata very high velocity. As the unburnt portion of the gas is compressed, its temperature and pressure may increase to such an extent that combustion will no longer proceed normally, but at so high a rate that the remaining gas burns almost instantaneously.- This extremely high rate of combustion constitutes detonation,commonly recognized by pinking or a metallic knocking sound.

The influence of the combustion chamber of an engine upon the phenomenon of detonation depends upon the cooling eect of the wall of the chamber upon the unburned portion of the burning gas,-particularly on that portion of the gas which burns last.

Harshness or smoothness of engine operation depends upon the rate of pressure rise,

which, at any instant, depends upon flame velocity, area of flame Spread and density of the unburned gas.

This invention consists of a combustion chamber so formed as to conduct heat away from that portion of an ignited gaseous charge that is last to burn at such a rate as to keep said last to burn portion of the gas below the temperature at which it will detonate; andfurther, of a combustion chamber having means for limiting the area of flame spread toward the end of the burning period so as to reduce the maximum rate of pressure rise and thereby improve smoothness of operation..

' In the accompanying drawing in which like parts are indicated by like reference characters throughout the several views:

1927. Serial No. 195,422.

Fig. l is a section through the head end of an engine embodying this invention, the

section having been taken on the line 1-1 of Figure 2, and

Fig. 2 is a section on line 2-2 of Fig. 1. For purposes of exemplification we have illustrated our invention in connection with v chamber 13, in the particular embodiment illustrated, extends completely over said cylinder bore and also has, as shown in the drawing, a considerable portion offset laterally, which is in communication with valve ports 14. The respective valve ports communicate also, as usual, with intake and exhaust conduits, not shown in the drawing, and valves 15 of poppet type open and close the ports as is usual.

In the illustrative example, combustion chamber 13 is elongated transversely of the cylinder axis, the valve ports being at that end of the chamber which is oiz'set from the cylinder. An ignition device, shown as a spark plug 16, is also disposed within the chamber, preferably extending through the roof of the offset portion at that side of the center of volume which is the more distant from the cylinder bore. Chamber 13 comprises a major and a minor portion the former of which has a relatively large volume capacity as compared with its surface area and the other a relatively small volume capacity as compared with its surface. The major 'portion of the chamber, which is that having large volume to surface ratio, is indicated at 17 in the drawing, while the minor portion, having a small ratio of volume to surface, is indicated at 18. The portion 17 includes by far the larger part of the volume of the chamber. The small volume to surface ratio of the minor portion is obtained by making the space at 18 relatively thin between the pressure surface of the piston and the roof of the chamber when the piston is at the extremity if its compression stroke. The major portion 17 is preferably of substantially even depth throughout its area, and the minor portion 18 is also of substantially even depth throughout its area.

An important feature of this -invention lies in the contour of that portion of the side wall of the combustion chamber which is adjacent f the opening affording communication beparallel .and ultimately flows smoothly tween the two portions of the chamber. This portion of the side Wall, as indicated at 19, has a re-entrant ballling surface. shown as a convexity, projecting toward the point of ignition 20, and the space 18, or minor portion of the combustionspace, is disposed at that portion of the chamber which is farthest removed from the point of ignition so that the last. gas to be burned' during the combustion.

perlod is that which is in contact with the baffling surface 19 and that which is disposed within said space 18.

The flame travels in all directions, of course, from the point of ignition. The flame front, therefore, as it approaches the re-entrant baflling surface will be curved along thegeneral direction of dotted lines 21 struck from the ignition point as a center, compressing all unburned gas in front ofy it during the later portion of the combustion period and crowding it into the space 18 which has such a large ratio of surface area to volume that the gas entering that space is cooled. The layer of unburned gas in front of the flame being compressed against the surface 19 is balled, and tends to divide and flow laterally in opposite directions as indicated by the arrows in Fig. 2, so that the unburned gas is smoothly deflected along the baflling surface, substantially therewith, giving up heat thereto,

into the relahaving been tively thin space 18 without thrown back against the flame front.

violently By reference to the drawing it will be ob:

served *that when the llame reaches the reentrant baling surface 19, it continues its advance with gradually reducing area of spread due to the cutting out effect of said re-entrant surface. By this means the rate of pressure rise is reduced` at the most critical4 time, namely when the flame velocity and density of the unburned gas approach their maximum values.

Although we have illustratedand described that form of chamber which we have found adapted to achieve the best results in accordance with our invention, it is to be understood that the particular form shown is exemplary only and not a measure of the scope of the claims.

We claim:

1. An internal combustion engine having a cylinder and reciprocating piston, a combustion chamber communicating with the cylinder, means to admit combustible mixture to the chamber and permit escape of products of combustion therefrom, and an ignition device providing a point of ignition disposed at one side of the center of volume of the chamber; the wall of said chamber at the other side of the center of volume having a re-cntrant baffling surface projecting toward the point of ignition.

2. An internal combustion engine having a cylinder and reciprocating piston, a combustion chamber communicating with the cylinder, means to admit combustible mixture to the chamber and permit escape of products of combustion therefrom, and an ignition device; said combustion chamber comprising a major portion of relatively large ratio of volume to surface, and a minor portion of relatively small ratio of volume to surface; the side wall of said combustion chamber adjacent the communication between said portions having a re-entrant baffling surface projecting toward the point of ignition.

3. The combination as defined in claim 2 in which the minor portion of the combustion chamber of relatively small ratio of volume to surface is opposed to the pressure surface of the piston.

4. The combination as defined in claim 2, in-which the minor portion of the combustion chamber of relatively small ratio of volume to surface is opposed to the pressure surface o f the piston that is farthest removed from the ignition device.

5. An internal combustion engine having a cylinder and reciprocating piston, a combustion chamber communicating with the cylinder, means to admit combustible mixture to the chamber and permit escape of products of combustion therefrom, and an ignition device providing a point of ignition at one side of the center of volume of the chamber; said chamber comprising a major portion of relatively large ratio of volume to surface, a minor portion of relatively small ratio yof volume to surface, and a re-entrant baffling surface disposed opposite the point of ignition at the opposite side of the center of volume.

n 6. An internal combustion engine having a cylinder and reciprocating piston, a combustion chamber communicating with the cylinder, said combustion chamber comprising a major deep portion of relatively large ratio of .volume to surface and having inlet and outlet vmajor and minor portions, said wall constitutlng a 're-entrant baiing surface projecting A vtoward the point of ignition.

7. A11 internal combustion engine having ,a cylinder and reciprocating piston,v a combustion' chamber communicating with the cylinder, said combustion chamber comprising a major deep portion of relatively "large ratio of volume to surface and having inlet and outlet valves therein and being of substantially even depth throughout its area, a minor shallow portion of relatively small ratio ofr volume to surface and of lsubstantially 4even depth throughout its area, an ignition device disposed' at one side of the center of volume of the chamber,v and a wall at the other side thereof adjacentthe junction between said major and minor portions constituting a reentrant bailng surface point of ignition. v

In testimony whereof we aix ourpsignatures.-

' WILLIAM B. EARNSHAW.

lROBERT N. JANEWAY.

projecting toward the 

